Electromyography

In the Electromyography (EMG) it is about the investigation of electrical functions of the skeletal muscles, based on the activity of which the muscle and nerve function can be assessed. This examination method is used whenever there is a suspicion of diseases of the peripheral nervous system, which includes muscles and nerves in the head, trunk and limbs.

What is electromyography?

Electromyography determines the electrical activity of muscles. Depending on the reaction of a muscle to rest or tension, it can be determined whether a certain disease is present.

The Electromyography determines the electrical activity of the muscles. Depending on the reaction of a muscle to rest or tension, it can be determined whether a certain disease is present.

While a muscle does not show any electrical activity when at rest, the corresponding muscle groups contract when the muscle cells are excited. This activity is measured using electrodes and then made visible and audible.

Healthy muscles react differently to sick muscles. The doctor can assess muscle functions as well as possible nerve and muscle diseases through the strength and type of current impulses that are active in electromyography.

Function, effect & goals

Before a Electromyography is used, a preliminary physical examination of the patient is necessary to make a suspected diagnosis. This is the only way to specifically examine the muscles. The area of ​​skin over the muscle to be examined is disinfected and then thin needle electrodes are inserted into the corresponding muscle. These measure the electrical voltage that the muscle generates when it is at rest and when it is contracted. This voltage is displayed on a screen in the form of voltage curves and also output via loudspeakers.

Electromyography is divided into three steps. First, the muscle activity is measured during the puncture and at rest. The activity is then tested with moderate muscle tension. In a final step, the muscle activity is determined with the greatest possible muscle tension. If the muscle or the associated nerve is damaged, a different electrical activity is determined. The muscle action potentials can be shortened or lengthened, for example in terms of their duration, and their potential curve can also decrease or increase.

Electromyography usually examines between three and five muscles. Using concentric needle electrodes, fluctuations in the potential of individual muscle groups can be recorded. Special needles are used to record individual muscle fibers (single fiber myography). Alternatively, surface electrodes can be placed on the respective muscle, but with this method no conclusions can be drawn about the activity of individual muscle fibers, since the action potential of whole muscles or several muscle groups is measured here. An electromyography takes about 15 to 30 minutes, during which the puncture site and puncture depth are changed several times.

The electrical activity patterns of the examined muscle resulting from electromyography make it possible to distinguish between muscular and nervous diseases. Therefore, this examination method is used, for example, to diagnose muscle weaknesses, muscle inflammation, nerve injuries and to differentiate certain nerve diseases (polyneuropathies). EMG is also used in cases of suspected spinal cord disease. Electromyography is often combined with electroneurography (ENG), which is used to measure nerve conduction velocity.

In the case of some diseases, electromyography can also be used to make prognostic statements regarding the healing process, for example in the case of nerve injuries as a result of an accident or pressure-related nerve damage and also in the case of certain types of muscle inflammation. In addition, various treatment methods for chronic or acute nerve or muscle inflammation sometimes require an exact electromyographic classification of the respective disease.

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Risks, side effects & dangers

Usually occur at the Electromyography no serious complications. The punctures of the needle electrodes, which are much thinner than the hypodermic needles for taking blood, can be compared with those of acupuncture.

The examined muscle or nerve fibers are not damaged by electromyography. However, the muscle may still be sore or numb for a few days after the exam. Electromyography should be avoided if the blood coagulation is disturbed by a disease or if you are taking anticoagulant medication due to the increased risk of bleeding.

Since the needles used in electromyography can forward skin germs into deeper layers of tissue, infections are possible, but occur extremely rarely. If the patient suffers from diseases that are transmitted by blood (AIDS, infectious hepatitis), this must be reported to the examiner so that he can take appropriate protective measures.